This invention relates to means for the delivery of agents into a living body. More specifically it relates to filaments comprising porous bioabsorbable polymers, which facilitate the implantation of living cells and other agents, such as drugs, into specific tissues, including skin and bone, for the purposes of site-specific drug or cell release, gene therapy, and the facilitation of the regeneration of tissue, including the regeneration of bone and hair tissue.
Current means for the delivery of agents such as drugs, growth factors, genetically modified cells, and the like into a living body include various pharmaceutical dosage forms, such as ingestable tablets, patches designed to deliver agents transdermally, and surgically implantable devices designed to deliver agents to an implant site. Early implantable devices were not bioabsorbable, and had to be surgically removed after they had been used for their intended purpose. More recently, implants of bioabsorbable polymers have been developed. Such implants are absorbed by the host in which they are implanted after, or in the course of serving their intended purpose. One such device, disclosed by Dunn et al. in U.S. Pat. No. 5,599,552 (“Dunn et al. '552”), is an implant of a porous core of a bioabsorbable polymer, surrounded by a non-porous surface skin of the bioabsorbable polymer. That particular device is designed for use in delivering a biologically active agent to a living host when implanted therein. The device disclosed by Dunn et al. '552 is also designed so that it can act as a matrix to promote tissue regeneration at an implant site. (Id.)
Two other types of implantable devices of bioabsorbable polymers are disclosed in U.S. Pat. No. 5,847,012 (“Shalaby et al. '012”). One such device consists of a bioabsorbable microporous polymeric foam with open-cell pores. The other such device consist of an implant with a modified surface, consisting of a surface layer of bioabsorbable microporous polymeric foam with open-cell pores. (Id.) The implants of Shalaby et al., '012 are designed to accept the agent to be delivered, such as a medicament or growth factor, and to deliver the agent to a living patient after implantation therein.
Textile technologies have also been adapted for use in making biodegradable woven fabrics as tissue engineering scaffolds. See Introduction of Peter X. Ma and Ruiyun Zhang in J. Biomed. Materials Res. 46(1):60-72 (July 1999). The diameter of the biodegradable fibers used to produce such woven scaffolds is about 15 μm. Ma and Zhang demonstrated that fibers with a considerably smaller diameter, ranging from 50 to 500 nm could be created from biodegradable aliphatic polyesters. The woven scaffolds of Ma and Zhang, and those described therein were designed for use as scaffolds, and not as means for delivery of agents to tissue.
The advantage of all the bioabsorbable devices described above was that they could be implanted into a living host and left in place to do what they were designed to do, without the necessity of removal therefrom. The devices would be absorbed by the host over time. Of the bioabsorbable devices disclosed in the references described above, only the device of Dunn et al. '552 is designed to act as both scaffolding and delivery agent. That device has limited flexibility, because of the way it is designed. What is needed is a bioabsorbable fiber or composite thereof, which is capable of being processed into a scaffolding for tissue formation, and which is capable of delivering agents to a living host when implanted therein. The present invention meets that need.
The present invention also meets a need for an inexpensive and relatively painless means for regenerating hair. Plastic surgery is one of the few means available to correct male pattern baldness, today. In that particular surgical procedure, the amount of permanently hair-bearing donor tissue available can significantly affect the feasibility and outcome of the procedure. In vitro growth techniques have been developed to increase the amount of hair follicle cells available for use in such procedures. See, e.g., Seigi Arase, et al. Tokushima J. exp. Med 36: 87-95 (1989); and Edoardo Raposio, et al. Plastic and Reconstructive Surgery pp. 221-226 (July 1998). What is needed is a relatively painless and inexpensive means for the regeneration of hair, one which does not involve plastic surgery or other painful and expensive implantation techniques, preferably, a technique which produces hair which looks realistic and similar to other hair on the same host. The present invention utilizes a modified form of the bioabsorbable polymeric means developed for use in implantable devices, as described above, to deliver hair follicle cells transdermally and to promote the regeneration of hair therein.
As is shown in the next section, below, the present invention provides a new means for the introduction of agents into a living host, a means which offers several advantages over known means in use today, such as those described briefly above.